imapsync - Console-based utility for migrating IMAP mailboxes.
MailStore - MailStore Home - A 100% free single-private-user desktop solution
OfflineIMAP - OfflineImap synchronizes email between an IMAP server and a MailDir or between two IMAP servers.
Intradyn Email Archiver - Orca Email Archiver provides email archiving solution for local government and business.
Fetchmail - The Fetchmail Project
Hornetsecurity Email Archiving - Hornetsecurity Email Archiving is one of the advanced software that offers long-term, unchangeable, and secure storage of important company information, data, and flies.